(1) Field of the Invention
This invention is directed to a method for testing the integrity of welds, or welded or other connections in a pressure vessel, and particularly, a process for pressure testing the integrity of such connections or welds at elevated temperatures using a pressurized gas composition formed within an indicator chamber wherein an inert gas is introduced to come into contact with and carry a marker component of an indicator composition, to locate flaws which may be present in the pressure vessel or welds.
(2) Brief Description of the Prior Art
In drilling an oil well, it is often necessary to install wellheads of various sizes of large diameter pipe. Several sizes of pipe or casing may be installed in a well. The well might include, as an example, a 36 inch driver pipe. There may also be a 20 inch casing, 13 and ⅜ inch casing and 9 and ⅝ inch casing. It is necessary to install a terminate flange or wellhead at every change of size. The wellhead is typically installed by first cutting the casing, preheating the casing, then welding the wellhead in place. The wellhead is necessary to mount other equipment or to otherwise install the next casing string. Often, this procedure requires cutting a very thick wall casing, even in the range of 1½ inch thick and thereafter making a multi-pass welded bead to attach the wellhead. To obtain a quality weld, the temperature of the pipe in the area of the weld must be raised to the welding temperature of the pipe or casing prior to actual welding. A typical welding temperature for pipe or casing material is in the range of 500.degree. F. Consequently, a tremendous amount of preheating is required to obtain a quality weld.
Preheating is often a problem, particularly for drilling rigs located at sea. In inclement weather, wind shields must be installed and a number of welders will position their torches on the casing and wellhead to preheated for perhaps 4 to 6 inches below the casing head in length to perhaps 500.degree. F. This is difficult and time consuming.
Certain devices have been provided heretofore to serve as pre-heaters. In U.S. Pat. No. 4,507,082 to Wardlaw, the inventor of the present disclosure, a preheating apparatus is described which heats the casing and wellhead from the interior. Other pre-heater devices are also available as typified by the patent of Jaeger, U.S. Pat. No. 3,082,760.
While a number of apparatus have been developed for preheating the casing and wellhead to welding temperatures, relatively little has been done in the area of testing or proving the integrity of the welds. The integrity of the welds connecting the wellhead or terminal flange to the casing, however, is critical to the safe completion of a well. When drilling an oil well, tremendous pressures may be encountered requiring that all connections or welds be leak-proof. This is particularly true for connection of the wellhead which includes other apparatus mounted thereon.
It has long been recognized that proving the integrity of welds, or connection points when assembling two or more units together to form a “pressure vessel” is desirable and necessary. To this end, terminal flanges or wellheads are provided with an internal circumferential groove, which groove is located between the inner and outer weld upon welding the wellhead to the casing. A port provides access to the groove. Thus, the conventional method for testing the integrity of welds includes the connection of a pressure pump to the port and pumping fluid into the groove and observing any pressure losses. Fluids such as oil, water, or antifreeze are typically used. Prior to injection of the fluid, however, the casing must be permitted to cool to approximately 200.degree. F. or less to avoid thermal shock at the weld. Rapid cooling can damage the metallurgy of the casing and wellhead material. The customary method of proving the integrity of welds is to permit the wellhead casing to gradually cool to a temperature of 200.degree. F. or less prior to injection of a fluid into the test groove to verify that no flaws or cracks are present in the welds. This procedure is very time consuming and in the event that flaws in the weld are located, the wellhead and casing must be reheated to the welding temperature to repair the flaws or cracks located in the initial welds. In addition, the test groove must be cleaned of injection fluid prior to reheating.
U.S. Pat. No. 4,596,135, issued to the present applicant, discloses a testing procedure and system which uses a marker gas of conventional nature, such as Freon. However, in recent years, Freon and other chlorine-containing halogenic gaseous substances have been prohibited as refrigerants and other commercialized uses by many nations in the world because of the belief that it destroys the protective ozone belt in the atmosphere. Other nations have, however, either not barred use of such gases or have not restricted their use to such a point that they cannot be used in very limited amounts for some uses.
Several other gas compositions have been suggested for many commercial applications, but their overall use and acceptance has been slow due to several disadvantages, not the least of which is the corrosive side effect that some of the newer gas compositions may have when exposed to some exotic metals sometimes found in industrialized applications.
In addition to problems associated with the use of chlorine-containing halogenic gases, any type of marker composition that is desired to be carried with an inert gas, such as nitrogen, has, prior hereto, been required to be provided in bottles or similar transportable containers which, in cases in which the weld to be tested is on an offshore well head, must be transported by boat to the particular work location. The transport of such bottles is costly, time consuming, and their stacking and storage on the platform or similar work location takes up valuable space.
The process and system of the present disclosure overcomes the disadvantages of prior art weld verification techniques, particularly where gases which have been proven to be environmentally dangerous have been utilized. It uses an inert gas, such as nitrogen, which is readily available in storage containers on the platform or other operations location, and which is used for may other applications. The need for bottled indicator compositions is eliminated by the use of a housing including a locator chamber wherein the inert gas is introduced into the chamber and caused to pass over or through or across means for receipt of an indicator composition, such as a removable or other surface means, such as a cloth, sponge, cotton balls, or the like, upon which the indicator composition has been previously impregnated.
The process of the present disclosure may be carried out at elevated temperatures thereby eliminating the time consuming cool down period prior to testing and the reheating period in the event remedial repairs to the welds required and by preferably incorporating a nonchloride-, nonchlorine-containing constituent as a marker. Conventional marker components containing a chlorine component or a mercaptan may also be used where permitted by law. Hydrocarbons, such as dielse and gasoline may also be used.